The use of inhalation devices to deliver carefully measured amounts of medication in order to dilute the bronchial passages is well known in the art. Inhalation therapy is preferred over oral and intravenous methods since a lesser amount of medication is required, the therapeutic effect occurs more rapidly, and there is a lower incidence of systemic side effects associated with use.
The first and foremost requirement of inhalation therapy is to ensure that a sufficient dose of medication reaches the lungs. Generally, the drug dose is deposited within the respiratory tract by a metered-dose inhaler. The metered-dose inhaler releases an aerosol spray consisting of large droplets of propellant within which the drug itself is encapsulated either as a powder or as a liquid. Since the drug particles and droplets are pressurized, their initial velocity upon discharge is extremely fast. Moreover, as a result of surface forces, the droplets and particles tend to cling together upon discharge so that large agglomerations form within the spray. Because the aerosol particles or droplets are large and the flow rate of the spray is rapid, most of the medication impacts in the oropharynx rather than in the bronchial passageways. Unfortunately, the sensation derived from oropharyngeal impaction may erroneously convince the patient that the required dose has been inhaled, when in reality the medication needed for bronchodilation has only been ingested. Consequently, the respiratory ailment remains untreated. The local impaction of the medication in the oropharynx can be especially deleterious when certain corticosteroid aerosols are utilized since local side effects such as oropharyngeal candidiasis or dysphonia may occur.
Deposition of the aerosolized medication in the lungs of the patient rather than his mouth would be more readily achieved if only the proper inhalation techniques were practiced. Several studies have shown, however, that a significant number of patients fail to either coordinate activation of the aerosol with inhalation, inhale slowly and deeply, or adequately breath-hold upon completion of inhalation. Consequently, a reduced amount of aerosol containing particles or droplets of medicine are deposited in the patient's lungs and, therefore, a reduced therapeutic effect results.
In order to ensure that a sufficient amount of the aerosolized drug deposits in the lungs of the user, even in patients with poor inhalation techniques, the prior art has developed several extension devices which attach directly to the metered dose inhalers. The extension devices provide an elongated chamber in which the propellant droplets can evaporate and large drug particles can settle so that only smaller and slower moving particles are ultimately inhaled by the patient. The reduced velocity and size of the particles allows the patient to slowly and deeply inhale the medication so that oropharyngeal impaction is reduced and bronchial deposition correspondingly increased.
Notwithstanding the increased lung deposition efficiency, however, other medically unrelated limitations arise when the extension devices are combined with metered-dose inhalers. The primary problem with extension devices is that they convey the image that the user is suffering from a serious medical illness. This false impression is derived from the fact that the majority of extension devices are bulky, cumbersome pieces of medical equipment, such as cylindrical chambers, multipiece chambers, cone shaped spacers or collapsible bags, which range in length from 10 centimeters to 25 centimeters and in volume from 100 centimeters cubed to 1000 centimeters cubed. Because of their large size and awkward shape, extension devices cannot be easily carried on the person of the patient and, instead, must be lugged around by hand or in a carrying bag as unobtrusively as is possible. Moreover, problems often arise during inhalation of the large droplets sized medications which cause the patient to wheeze and cough, thereby drawing unwanted attention to his activities. Consequently, a patient may forego a scheduled treatment if the time of inhalation requires the use of the extension device in public in order to avoid the embarrasment of stigmatization frequently associated with illness in today's society. Although some collapsible extension devices are currently available which can be carried in a pocket or purse, these collapsible devices must stil be fully extended in order to allow the delivery of the desired medication. Hence, the prior art still lacks a small, portable metered-dose inhaler which is neither cumbersome nor large, yet which can effectively reduce the size and velocity of medicinal aerosols discharged therefrom.